We've seen a number of hyperthyroidism cases over the years. In fact, though the reasons are unclear, studies show that the incidence of overactive thyroid glands in cats have markedly increased over the last 25 years. Feline hyperthyroidism is treatable if caught early; however, serious medical conditions can result if this disease is left untreated.

All of the symptoms associated with feline hyperthyroidism involve an increase in thyroid hormone. Common symptoms include:

Increased appetite with weight loss

Hyperactivity

Vomiting

Diarrhea

Increased water consumption

Frequent urination

However, as the cases below illustrate, you can help your hyperthyroid cat lead a normal, healthy, and happy life:

Treatment

Pros

Cons

Methimazole

Medication readily available

Inexpensive in short-term

No anesthesia or surgery

No hospitalization or special facilities required

Treatment is reversible, if needed

Development of hypothyroidism very rare

Preferred in cats with kidney failure or other serious disease

Use prior to radiation or surgery to stabilize cat

Not a cure; the adenoma will continue to grow

Lifelong therapy necessary

Medication may need to be given more than once daily

May be difficult to give medication

Medication has side effects some cats cannot tolerate

Periodic blood work required

Surgery

Cures the condition unless all of the abnormal tissue is not removed

Approximately the same cost as several years of methimazole

Short hospitalization

No need for daily medication

Requires anesthesia

Cat must be a good surgical candidate

Post-operative complications can occur to parathyroid gland or nerves in the area

Could rarely cause hypothyroidism

Not possible if thyroid tissue is located within the chest

Recurrence possible

Radiation

No anesthesia, sedation or surgery

All abnormal tissue is treated

No need for daily medication

Does not destroy healthy tissue or other organs

Normal thyroid function returns within a month

Preferred if malignancy present, or thyroid tissue located within the chest

Availability limited

Most expensive alternative: over $1,000

Specialized facility required

Hospitalization and quarantine required

Treating other diseases during initial days following treatment is not possible

In rare cases may need to be repeated

Could rarely cause hypothyroidism

Chemical Ablation

Short anesthesia time

Short hospitalization

No need for daily medication

Specialized facility not required

Requires anesthesia

Post-operative complications can occur to nerves in the area

Not possible if thyroid tissue is located within the chest

Effects may be short-term, and procedure may need to be repeated multiple times

Case One: Fuzzy GoesFuzzy, an eight-year-old white Persian mix, was known for being active, healthy, and fastidiously clean. So we were naturally concerned when Fuzzy's owner, Alice, brought him in to see us because lately he'd been drinking more water and had begun urinating outside the litterbox in the house. Alice was worried that Fuzzy had a urinary tract problem - which is common in neutered male cats.

But during our physical exam of Fuzzy, we noticed something amiss with the thyroid gland in his neck. In fact, the gland was so enlarged we could feel the left lobe of the gland, but could not find the right lobe. A blood test showed an excessive amount of thyroid hormone (known as thyroxine or T4 in blood tests), which confirmed that Fuzzy had an overactive thyroid gland.

We discussed Fuzzy's treatment options with Alice. Initially, we recommended drug therapy to control Fuzzy's enlarged thyroid gland. But Alice didn't like the idea of giving Fuzzy medicine every day for the rest of his life - after all, Fuzzy was relatively young. Nor did she like the costs that would add up over years of thyroid medicine use, especially since medicine can control hyperactive thyroids but it does not cure hyperthyroidism.

Alice finally opted for surgery to remove the abnormal thyroid tissue. Unlike medications, successful thyroid surgery can cure feline hyperthyroidism. However, the surgery could possibly have to be repeated if additional abnormal tissue growth should occur. Thankfully, Fuzzy's abnormal tissue was contained in the immediate area and surgical removal was fairly easy. After a short recovery time, Fuzzy was soon back to his normal antics and Alice was consulting us on a different matter - how to best let Fuzzy release all his playful energy.

Case Two: Grigio the HungryMichael had never seen his sleek gray, 13-year-old cat, Grigio, so hungry. But Grigio seemed ravenous all the time. In fact, Grigio would whine at the closed pantry door where his food was kept, jump onto the counter while his meals were prepared, and gobble down his food as soon as it was ready. More mysterious, however, was that Grigio was losing weight in spite of his increased appetite.

Needless to say, we were just as worried about Grigio's health as Michael. We ordered a complete blood workup, including a T4 test. The test results showed that Grigio's T4 levels were elevated, as were his kidney values: blood urea nitrogen (BUN) and creatine. The high T4 levels told us that Grigio's thyroid was hyperactive, while the elevated BUN and creatine levels indicated potential kidney disease.

There was a chance that Grigio's overactive thyroid could also be causing his kidney troubles. While we monitored his kidney function, however, we wanted to start treating his hyperthyroidism. We suggested Michael use the drug methimazole to control Grigio's thyroid activity. This would also let us monitor and treat his kidney problem. Plus, considering Grigio's age, drug therapy was less obtrusive and less costly than other treatments for hyperthyroidism

Case Three: Gladys the Cat ClownGladys is an active, young spayed female calico owned by Rodney, who had recently retired. At first, Rodney was worried about what he was going to do with all his time. But since he adopted Gladys, his days had been filled with companionship and laughter - especially since Gladys is known as a bit of an antic-filled cat clown.

But Rodney became worried when Gladys began keeping him up at night with her constant activity. So he brought her into us to have her checked out. Though Gladys appeared physically healthy, we still ran some precautionary blood tests and found an elevated T4 level in Gladys' blood and recommended treatment for an overactive thyroid.

Since Gladys was so young, Rodney was interested in radioactive iodine therapy. With this treatment, radioactive iodine is given to the cat intravenously. The radioiodine then becomes concentrated in the thyroid gland and destroys the malfunctioning tissue but does not affect any healthy thyroid tissue. This treatment can be expensive and Gladys would have to remain at the clinic for a week or two until the radioactive material was cleared from her body. We did not have the equipment to perform this therapy so we gave Rodney and Gladys a referral to a larger clinic in Madison. The prognosis for cats that receive this treatment is excellent. Gladys responded favorably and went on to live a normal, active life.

All three cats are doing extremely well now and their owners have reported no further signs or complications.

A new treatment, called "ablation" is being investigated. With this treatment, ultrasound is used to identify the thyroid gland, which is then injected with a chemical or exposed to heat via high radiofrequency to kill the abnormal cells. Although the procedure requires anesthesia, the treatment takes less than 15 minutes.

Q. What is the thyroid gland?
A. The thyroid gland is a small, butterfly-shaped gland in the neck. The thyroid gland produces the major thyroid hormone called thyroxine (T4) and a small amount of another hormone, triiodothyronine (T3). These hormones regulate the body's metabolic rate and affect every system in the body. The production of the thyroid hormones is controlled by the hormone called thyroid-stimulating hormone (TSH). TSH is produced by the pituitary gland, which is found at the base of the brain.